1. Field of the Invention
The invention relates to an X-ray device comprising a number of components to each of which is assigned a data transmission node working by the CAN protocol whose data input and data output are in mutual communication with other data transmission nodes via transmitters and receivers, the data transmission nodes being connected to the relevant associated components through connection lines.
2. Description of the Related Art
Such an X-ray device is known from DE-A-40 25 834, corresponding to U.S. application Ser. No. 07/738395 to the same assignee as the present application.
The CAN protocol is known inter alia from the Intel publication "82526 Serial Communications Controller Architectural Overview"(ordering number: 270678001) and from the journal "Elektronik"(no. 25, 08.12.1989, pp. 79-83 and no. 12, 08.06.1990, pp. 109-114). In the CAN protocol, data are defined by the two logic levels "dominant" and "recessive". A dominant bit is obtained when one or several (data transmission) node(s) transmit(s) a dominant bit. A recessive bit is obtained only when all nodes generate such a bit. The information is coded in an NRZ code, i.e. the logic level does not change in the case of several consecutive bits of the same level.
According to the CAN protocol, each node can transmit data to each of the other nodes at any time (Multimaster principle) without having to wait for an authorization to transmit. The exchange of information accordingly takes place very quickly, which is essential for at least some components in an X-ray device.
According to the CAN protocol, each message (messages are also referred to as "communication objects" in the CAN protocol) comprises a so-called identifier which characterizes the nature of the data to be transmitted and which is transmitted following a start bit. When several data nodes start transmitting simultaneously, those nodes which transmit a recessive bit during transmission of the identifier, but which received a dominant bit, break off their transmission, so that only one data node is capable of transmitting the subsequent data of the message. Those nodes which received the data and test words of the transmitter correctly transmit an acknowledge signal (ACK signal) before the relevant transmitting node has ended a transmission. Those nodes which detect a faulty transmission transmit an error signal which causes all other nodes also to transmit an error signal and the transmitting node to break off the transmission and to repeat it. As a result, data nodes working in accordance with the CAN protocol have a high transmission speed as well as a high transmission reliability.
In the known X-ray device, the individual data transmission nodes are interconnected by means of optical waveguides combined into a loop. The time available for the transmission of a bit must be longer than the time required by the optical signal for reaching the last node in the loop jumping from node to node. The advantages of the high data transmission speed provided by the CAN protocol are partly wiped out again thereby. In the known device, moreover, difficulties may arise when an additional component is to be included in the x-ray device (in such a case an additional data transmission node must be included in the optical waveguide loop by means of additional waveguides), and when components perform strong movements relative to other components, because the associated data transmission nodes are in connection with the other data transmission nodes via optical waveguides.